Recently, due to an increase in the awareness about ecology, there is an increasing demand for a smart glass with a built-in light-modulating function which modulates the light shining into the inside of rooms and the like.
For the smart glass contributing to improving the air-conditioning energy efficiency, an electrochromic element exhibiting a function of switching a transparent state and a light-shielding state (nontransparent state) is used. Through controlling the influence of natural light to decrease the air-conditioning load by the light-modulating function regarding the switching of the states, the electric power use amount is reduced.
As an example of the practical use of the glass to which the electrochromic element is built-in, the technical content disclosed in Patent Document 1 or 2, for example, is known.
Patent Document 1 discloses a window glass capable of switching a transparent state and a light-shielding state through changing the voltage to be applied to two transparent electrodes disposed in opposition to one another via a variable member (an electrochromic element).
The electrochromic window glass disclosed in Patent Document 2 employs a structure in which two glass plates on which a transparent conductive film and a film of an electrochromic material are coated in this order are disposed with each of the film sides being opposed to each other and the two glass plates are isolated from each other via an electrolyte and a counter electrode. The electrochromic window glass can be employed as windows of buildings and automobiles, which makes it possible to control the amount of solar heat captured into the inside thereof by the effect of the electric field for the counter electrode.
In the meantime, there has been an increasing demand for being able to arbitrarily achieve a state where the viewing field for the front direction is maintained while shielding the light of the other directions. For example, there is a demand for making it possible to shield the light that makes incident from the upper oblique directions such as the sunlight while maintaining the visibility from outside or inside.
As a technique for satisfying such demand, proposed is a light-ray direction control element that is provided with a light-modulating function which switches the visible range of a display between a wide viewing field mode (a state where visual recognition can be achieved in a wide range) and a narrow viewing field mode (a state where visual recognition can be achieved only in a narrow range).
As such light-ray direction control element, there is a light-ray direction control element 210 that employs the structure in which: a light transmissive regions 240 are formed by exposing, developing, and heating a transparent photosensitive resin layer by using two transparent substrates 221 and 222 disposed in opposition to one another as in a sectional view shown in FIG. 29, for example; and an electrophoretic element 250 is disposed between the light transmissive regions 240. In this case, transparent conductive films 231 and 232 are formed, respectively, between each of the transparent substrates 221, 222 and the light transmissive regions 240.
As described, in the light-ray direction control element 210 where the electrophoretic element 250 is disposed between the light transmissive regions 240 of a high aspect ratio arranged two-dimensionally independently on the transparent substrate 221, the emission state of light (incident light) 450 is switched by arbitrarily achieving the narrow viewing field mode shown in FIG. 29A and the wide viewing field mode shown in FIG. 29B through controlling the dispersion state of the electrophoretic element 250 with the electric field applied from outside via the transparent conductive films 231 and 232.
Further, as another structural example capable of such switching processing, a light-ray direction control element disclosed in Patent Document 3 is known. That is, as in a sectional view shown in FIG. 30, a light-ray direction control element 310 includes: a transparent substrate 321; a transparent conductive film 331 formed on the surface of the transparent substrate 321; a plurality of light transmissive regions 340 formed to be isolated from each other on a top surface 331a of the transparent conductive film 331; electrophoretic elements 350 disposed between each of the light transmissive regions 340; and another transparent substrate 322 that includes another transparent conductive film 332 on a face opposing to each of the light transmissive regions 340.    Patent Document 1: Japanese Unexamined Patent Publication Sho 59-191017    Patent Document 2: Japanese Patent No. 3399967    Patent Document 3: U.S. Pat. No. 7,751,667
However, the light-modulating functions disclosed in Patent Document 1 and Patent Document 2 are the techniques for achieving only the two kinds of the states that are the transparent state and the light-shielding state. Especially in the light-shielding state, the entire surface of the glass is equally light-shielded so that the visibility through the glass becomes deteriorated.
Further, when the optical density at the time of shielding the light is set to be low in order to minimize the deterioration in the visibility in the light-shielding state, the light-shielding effect by the light-modulating function cannot be acquired sufficiently.
In addition, even though the light-modulating function disclosed in Patent Document 3 can achieve a wide visible range state or a narrow visible range state at arbitrary timing, at least the front viewing field is maintained. That is, the entire surface of the substrate cannot be light-shielded, so that the complete light-shielding characteristic cannot be secured.
The present invention is designed in view of such shortcomings of the above-described related techniques. It is particularly an object of the present invention to provide a light-modulating element capable of effectively adjusting and controlling the transmission state of the transmitted light in accordance with the demand and the changes in the use environment and provide a smart glass on which the same is loaded.